1. Field of the Invention
This invention relates to a hybrid drive unit provided with two kinds of prime movers as a power source for driving a vehicle, and more particularly, to a control device for a hybrid drive unit, wherein a second prime mover is connected through a transmission to an output member, to which a power is transmitted from a first prime mover.
2. Related Art
An example of a control device of hybrid drive unit of this kind is disclosed in JP-A-2002-225578. In this publication, there is described the hybrid drive unit, in which an engine and a first motor generator are connected to each other through a synthesizing/distributing mechanism composed of a single pinion type planetary gear mechanism while an output member is connected to the synthesizing/distributing mechanism in a torque transmittable manner, and in which a second motor generator is connected to the output member through a gear shift mechanism.
According to the hybrid drive unit described in this publication, therefore, a torque synthesized from an output torque of an engine and a torque of the first motor generator in accordance with a gear ratio of the single pinion type planetary gear mechanism appears on an output shaft, and an engine speed can be controlled by the first motor generator. Therefore, it is possible for the engine to be driven for the optimum fuel consumption thereby to improve a fuel consumption of a vehicle. Moreover, the torque can be applied to the output shaft, by generating an electric power (i.e., regeneration of energy) by the first motor generator so as to drive the second motor generator by the electric power generated, when the engine is being driven at the optimum fuel consumption. Therefore, sufficient driving force can be obtained without deteriorating the fuel consumption. Moreover, the torque outputted by the second motor generator can be raised and transmitted to the output shaft, by having an gear ratio to be set by the transmission greater than “1”. And in case the gear ratio is reduced (e.g., in case the transmission is set in a high speed stage), a speed of the second motor generator can be decreased so that the second motor generator can be changed into a low power type or a small size type.
The aforementioned hybrid drive unit is so-called “mechanical distribution type”, and the same type of the hybrid drive unit is disclosed in JP-A-2000-295709. The unit disclosed in this publication is so constructed as to control the torque of individual motor generator when the gear shift is executed by the transmission.
Also, a motor-driven vehicle, in which the output torque of the electric motor is transmitted through the transmission to the output shaft is disclosed in JP-A-6-319210. In the vehicle disclosed in this publication, the torque of the electric motor and an apply pressure of the clutch at the shifting time is controlled with judging the situation at the shifting time.
In JP-A-2000-295720, moreover, there is described a so-called “series type hybrid drive unit”, in which a electric generator is driven by the engine, and in which the electric motor is driven by an electric power generated by the electric generator. In this device, the gear shift is inhibited in case of driving on a downhill having a gradient steeper than the predetermined value.
In JP-A-9-9414, still moreover, there is described a hybrid drive unit, which is constructed to change a shift point on the basis of a remaining amount SOC (i.e., State of Charge) of the battery. Also, in JP-A-9-233606, there is described a hybrid drive unit, in which the vehicle is driven by the motor with reducing the gear ratio in the case the charging amount SOC remains sufficiently, and in which the vehicle is driven by the engine with greatening the gear ratio in the case the charging amount SOC does not remains sufficiently, on the contrary.
In the aforementioned so-called “mechanical distribution type” hybrid drive unit, as described in JP-A-225578, the second motor generator is connected through the transmission to the output shaft. Therefore, in case that the gear shift is made under the state where the second motor generator is controlling the run into a power mode or a regenerative mode, a transmission torque by the transmission falls during the shifting operation. As a result of this, the output shaft torque is changed and it may cause shocks. On the other hand, this hybrid drive unit is constructed to synthesize the output torque of the engine and the torque of the first motor generator by a planetary gear mechanism, as they are outputted, so that the output shaft torque can be controlled by the first motor generator. Therefore, it is considerable to control the first motor generator thereby to suppress or prevent such torque change at the shifting time by the transmission.
Since the first motor generator and the engine are connected through the planetary gear mechanism, as thus far described, the torque which acts on the engine as a reaction is changed when, for example, the torque of the first motor generator is changed in order to raise the output shaft torque. The engine does not output the torque when the vehicle is driven by the torque of the second motor generator with the engine being halted. Therefore, in case that the torque of the first motor generator is changed so as to suppress the reduction of the output shaft torque at the shifting time in the transmission, the torque to rotate the engine backward may act on the engine. Because it is not preferable for the engine to be rotated backward, after all, it is not possible to suppress the reduction of the output shaft torque as might otherwise accompany the gear shift in the transmission, when the vehicle is running in so-called “EV run” in which the vehicle is run by the torque of the second motor generator.
On the other hand, aforementioned first motor generator and second motor generator can perform as either the electric motor or the electric generator, so that the fall of the output shaft torque can be suppressed by controlling the torque of those motor generators variedly at the shifting time in the transmission, when the vehicle runs with using those motor generators. However, in case of raising a positive torque, which is to be outputted by any of those motor generators, the output of an accumulator device such as the battery has to be raised. In order to raise a negative torque, on the contrary, it is necessary for the accumulator device to accept the generated electric power.
Specifically, the accumulator device participates in the torque control by the motor generator, but a capacity of the accumulator device is limited. Therefore, the accumulator device cannot drive the motor generator or raise the output torque thereof, when the stored amount of electricity (charging amount) is low. When the stored amount of electricity (charging amount) is almost full, on the contrary, the accumulator device cannot accept the electric power so that the negative torque by the regenerative control of the motor generator cannot be raised. This kind of restriction on the control of the motor generator caused by the accumulator device may arise not only from the stored amount of electricity (charging amount), but also from the temperature etc. After all, the control of the motor generator is restricted according to the situation of the accumulator device functioning as an energy source of the motor generator, even if there is no trouble on the motor generator. As a result, the change of the output shaft torque at the shifting time in the transmission cannot be suppressed, and this makes it probable that the deterioration in the shocks cannot be prevented.